Such an elevator system is in particular an elevator system which comprises one shaft in which a plurality of cars can be moved separately. In particular, at least one additional car can be moved above and below at least one car. In particular, this method of a plurality of cars substantially independent of each other in a shaft is a sequential operation in the sense of the present invention. In the prior art, such an elevator system is known for example from the document EP 1 562 848 B1.
Moreover, an elevator system as mentioned above is in particular an elevator system with a shaft system comprising a plurality of shafts, wherein the elevators can be moved in particular in a circulating mode as a sequential operation. The movement in a sequential operation occurs in particular in that several cars travel upward together in at least one shaft of the shaft system, travel from this shaft into at least one additional shaft and in this at least one additional shaft they travel downward together. In such an elevator system it is provided in particular that usually several cars are moved at any one time in each of the shafts of the shaft system. Such an elevator system is known in the prior art, for example from the document EP 0 769 469 B1.
The sequential operation of the cars of such elevator systems requires a particular design of the safety system of the elevator system, since a collision between cars must absolutely be prevented. In order to prevent a collision between cars, it is known, for example from the document WO 2004/043842 A1, how to monitor the absolute distances between the immediately neighboring cars. If the distance falls below a predefined value for a critical spacing between two cars, a measure is taken to avoid a collision of the cars. Such a measure may be the triggering of a safety mechanism of the car for example, especially the triggering of a catching device of the car.
According to document EP 0 769 469 B1, collisions between cars cannot be prevented simply by a large spacing. It is therefore proposed in document EP 0769 469B1 that each car has its own safety module in addition to its own drive unit. This safety module can trigger braking processes both for the corresponding car and for neighboring cars. The safety module computes from the current movement data of all cars of the elevator system the required braking behavior of the cars.
One problem known from EP 0 769 469 B1 is that the data volume required for this computation taking account of the current movement data is so large that an ongoing transmission and processing of this data is not possible, at least not with reasonable technical expense, so that EP 0 769 469B1 proposes working with a dynamic elevator model.
This means, for a decentralized safety system in which the spacing monitoring of the cars occurs locally at the cars, the above-described principle either involves an unmanageable communication burden between the safety modules of the cars of an elevator system. The technical expense in handling so large a communication burden can be realized at most with very large technical expense. Alternatively, elevator models which best approximate the actual elevator operation need to be developed and serve as the basis for the computations of the braking processes, which involves large expense. Furthermore, each time the model must be adapted to the actual circumstances, such as the respective number of cars for example.
Against this background, one problem of the present invention is to improve a method for the operation of an elevator system which comprises a shaft system and at least three cars, especially so that possible collisions of cars can be recognized early on, wherein the recognition should advantageously be done by means of a decentralized design of the safety system. Preferably, the data volume to be transmitted here should be as low as possible. Moreover, an easy transferability of the method to elevator systems of different design should preferably be possible.